1. Field of the Invention
This invention relates to polymeric compositions. More specifically, this invention relates to polymeric compositions for high speed manufacturing of thin wall packaging containers.
2. Background of the Invention
Polypropylene materials, formed by catalysts such as Ziegler-Natta or metallocene compounds, are among the most versatile and commonly used thermoplastics in the world today. These materials are formed into a variety of end-use articles ranging from automobile parts to food containers using a number of plastics shaping processes. One such process is injection molding.
In injection molding, a plastic component is formed from molten polymer resin that is injected into a mold cavity. The molten resin is held in the cavity for a sufficient time period to allow the part component to form. The time required for the molding to cool and be removed, or the cooling phase, is an important factor in the production time and therefore in the manufacturing efficiency. Resin properties such as thermal expansion and compressibility determine the extent to which a molten resin will undergo dimensional changes during the cooling phase. These dimensional changes that occur during the cooling phase are termed shrinkage.
During the manufacturing of plastic components, shrinkage results in a volume difference between the initially cast mold and the final molded article. If the dimensional changes are uniform the shrinkage is termed isotropic while varying dimensional changes are termed anisotropic or differential. The shrinkage whether isotropic or anisotropic must be accurately accounted for in the manufacturing of plastic components in order to obtain end-use articles of the correct dimensions.
Given the foregoing discussion, it would be desirable to develop a method of manufacturing end-use articles from a polymeric resin having a reduced amount of shrinkage with a short cooling phase. It would also be desirable for this polymeric resin to display enhanced mechanical properties such as impact strength and stiffness.